1. Field of the Invention
The invention presented herein relates to bi-directional facsimile subscan drive controls for drum-type facsimile machines and more particularly to such controls using a single stepping motor electrically controlled for operation at any of several rates for moving the scan head in one direction during a scanning operation and at a much higher rate in the opposite direction for returning the scan head.
2. Description of the Prior Art
Drum-type facsimile machines use a drum on which the original or copy paper to be scanned is mounted. During a transmitting or receiving operation, the drum is rotated by one motor relative to a scan head to provide the main scan, while the scan head is driven axially of the drum in a continuous manner under the control of a second motor to provide the subscan for the machine. In this manner a helical scan is made of the material carried on the drum. Once the subscan, which is carried out at a relatively slow rate, has been completed, the scan head is usually automatically returned to its start position at a much higher rate to place the machine in condition for the next transmitting or receiving operation.
It is desirable that the return of the scan head be done automatically and before the operator normally has had time to remove the original or copy from the drum and secure another to the drum. Prior art facsimile machines have used tension devices, such as a spring, to provide the force for the return for the scan head. The tension device is arranged to be placed under tension as the subscan operation proceeds. The subscan drive is uncoupled from the scan head at the completion of the subscan allowing the tension device to return the scan head to the desired starting point for the next operation of the machine. Other prior art machines have used a separate drive mechanism which is engaged for returning the scan head at the completion of the subscan. U.S. Pat. No. 3,764,741 to John H. Long and U.S. Pat. No. 3,927,256 to Sakae Fujimoto are examples of the prior art arrangements that have been described.
The subscan drives of the prior art require special clutching arrangements which are subject to failure and spring type return mechanisms are known to present service problems.